Actions of disopyramide on potential reentrant pathways and ventricular tachyarrhythmias in conscious dogs during the late post-myocardial infarction phase.

The effect of intravenous disopyramide (plasma level 3.7 +/- 1.6 micrograms/ml, mean +/- standard deviation) on reentrant ventricular tachyarrhythmias was studied by programmed ventricular stimulation in 11 conscious dogs 3 to 8 days after experimental myocardial infarction. Sustained ventricular tachycardia (VT) was induced in 4 dogs (mean cycle length 173 +/- 14 ms) and nonsustained VT in 7 (8 +/- 4 beats, mean cycle length 136 +/- 18 ms). Disopyramide prevented induction of VT in 1 of 4 dogs with sustained VT and 3 of 7 with nonsustained VT, and increased VT cycle length by more than 30% in 2 dogs with sustained VT and 2 of 7 with nonsustained VT. Disopyramide prolonged refractoriness in the infarct zone, measured by analysis of electrograms from an implanted "composite" electrode, by 38 to 53%, depending on the mode of pacing. These values were significantly greater than the increase produced by disopyramide in ventricular effective refractory period (13 +/- 12%), QRS duration and QT interval. Disopyramide has a selective effect on potential reentry circuits in ischemic myocardium, and prolongs refractoriness in abnormal myocardium to a greater extent than its effect on the normal ventricle.